1. Field of the Invention
The invention relates to a cam cap for an internal combustion engine and an oil passage connection structure of a cam cap for establishing an oil passage connection with a cylinder head cover.
2. Description of the Related Art
Japanese Patent Application Publication No. 2003-227321 (JP-A-2003-227321) proposes a cam cap (called “cam bracket” in the publication) having an intake side cam cap portion and an exhaust side cam cap portion that are integrally formed to support the intake camshaft and the exhaust camshaft of an internal combustion engine on journal bearings formed on the cylinder head or the cam housing, respectively. This cam cap involves oil passages through which hydraulic oil is supplied to and drained from a single oil control valve (called “hydraulic pressure control valve” in the publication) provided in the cylinder head cover, and hydraulic oil is supplied, at a pressure adjusted by the oil control valve, to only one of the camshafts. More specifically, the pressure-adjusted hydraulic oil is supplied to a variable valve timing mechanism provided at one end of one of the camshafts to adjust the operation timing of the exhaust valves or the intake valves as needed. Note that, in the specification of the present invention, the phrase “pressure adjusting” includes starting and stopping the application of hydraulic pressure, as well as adjusting the hydraulic pressure level.
According to Japanese Patent Application Publication No. 2003-227321, the joint between the oil passage connection face of the cam cap and the oil passage connection face of the cylinder head cover is sealed by a gasket that serves also as an oil filter. Thus, the gasket is retained in position by being sandwiched between the flat oil passage connection face of the cam cap and the flat oil passage connection face of the cylinder head cover.
When using such a gasket used also as an oil filter, however, it is necessary to provide a locating post on the oil passage connection faces as described in Japanese Patent Application Publication No. 2003-227321. Thus, the outline of each oil passage connection face becomes complicated and large in size.
To avoid such a problem, one option is to provide a separate oil filter and form a gasket groove in the oil passage connection face and fit a gasket in the gasket groove. In this case, the respective parts can be located in their positions by simply fitting a gasket in the gasket groove and the shape of the structure around the oil passage connection face does not become complicated and large in size.
However, the difference between the hydraulic pressure in one of two pressure-adjusting oil passages and the hydraulic pressure in the other varies as the valve timing control by the oil control valve is repeatedly switched between the mode for advancing the valve timing and the mode for retarding the valve timing and as the operation for the valve timing control is repeatedly activated and stopped. This hydraulic pressure difference may cause the gasket to slide in the gasket groove, and it may cause wear of the gasket.